Conservative statistics indicate that about 14% of women and 22% of men have had affairs sometime in their marriage [Laumann et al. “The Social Organization of Sexuality: Sexual Practices in the United States”; University of Chicago Press: Chicago, page 216, 1994]. According to a recent study by the Centers for Disease Control, about 4% of both married men and women had more than one sexual partner in the previous twelve months [Mosher et al. “Sexual Behavior and Selected Health Measures: Men and Women 15-44 Years of Age, United States, 2002,” Advance Data, 362, page 10, 2005]. This figure rises to 15% in the case of unmarried couples cohabiting. These data indicate that infidelity is a significant problem in the United States, and there exists a need to objectively test spouses for sexual activity. For women, one such test is for the presence of semen.
When a man has sexual intercourse with a woman, semen is deposited into the woman's vagina. Immediately after intercourse, most of the semen flows back out, but some is retained in the vagina and slowly is discharged over a period of several days [Hooft et al, Am. J. Forensic Med. Pathol., 18, pages 45-49, 1997]. Semen has over 900 identified proteins [Pilch et al, Genome Biology, 7(R40), 2006] among which are semenogelin I and II (gel-forming proteins produced by the seminal vesicles), prostate-specific antigen (PSA, a protease which breaks down semenogelin), and acid phosphatase (which breaks down spermatozoa cell membranes) [Tanaka et al, FEBS Lett., 571, pages 197-204, 2004]. These proteins can be identified by immunochromatographic assay, which forms the principle of the PSA and semenogelin tests. Acid phosphatase can be detected by the classic test first reported by Babson et al in Am. J. Clin. Pathol., 32, pages 88-91 (1959), which forms the principle of the AP test in the present invention. This test relies on the catalytic hydrolysis of 1-naphthyl phosphate to form 1-naphthol, which in turn reacts with an aryl diazonium salt, forming an intensely colored azo dyestuff. In addition to proteins, semen also has unusually high concentrations of zinc (100-200 mg/L v. 1 mg/L in plasma) [Owen et al, J. Androl., 26, pages 459-469, 2005]. Zinc (like AP and PSA) is produced by the prostate gland and after ejaculation, 50% is bound to seminal vesicle proteins. Zinc acts to stabilize DNA inside spermatozoa, is a cofactor in enzymatic reactions and also may catalyze the gel-forming reaction between semenogelin I and II. Semen may be detected by the modified zinc test of Hooft and van de Voorde [Hooft et al, Forensic Sci. Int., 53, pages 131-133, 1992].
The semen flowing back out of a woman's vagina (“backflow”) is deposited on her underwear or absorbent pad. These items conveniently can be tested with the AP test strip described in this invention. The strip also can be used to test stains on other fabrics and surfaces.
All stains on women's undergarments are not semen. In fact, asymptomatic women produce, on the average, 1.5 g of vaginal fluid per day, which typically leaves a white-to-beige stain [Beckmann et al. “Obstetrics and Gynecology, Second Edition”; Williams & Wilkins: Baltimore, page 294, 1995]. Semen stains, on the other hand are white and appear mainly just after intercourse. The next day, discharge of residual semen may not be visible at all. Thus, it is impossible to tell visually whether a suspicious stain is semen, and men must rely on analytical methods of detection such as that described in the present invention.
Other methods for semen detection have been described. Immunochromatographic test strips for PSA, first described by Yoshiki [An et al, Cancer Lett., 162, pages 135-9, 2001] are commercially available from several suppliers and have been validated for use in forensic investigations [Laux et al, online, retrieved 2008]. A similar test for semenogelin recently has been described [Pang et al, Forensic Sci. Int., 169, pages 27-31, 2007]. Test methods for acid phosphatase (AP) also have been described, for example as a test strip in U.S. Pat. No. 5,981,206 (Arter et al) and as a solution in U.S. Pat. No. 3,002,893 (Babson) and U.S. Pat. No. 6,764,856 (Holmes et al). Machery-Nagel also manufactures a test paper for the determination of AP, but they do not disclose the chemistry employed [Machery-Nagel, online, retrieved 2008].
Recently Hooft et al showed that the modified zinc test was more sensitive and specific for the detection of semen than the classic acid phosphatase test [Hooft et al, Am. J. Forensic Med. Pathol., 18, pages 45-49, 1997], although the ready availability of AP test strips may be a reason why zinc strips were not more widely adopted.
Although test methods for AP have been described, a test strip assembly which allows for the ready determination of semen, easy visualization through a transparent cover, and an adhesive backing which allows for convenient placement in a notebook has not.